Arrangement for mounting an optical element

ABSTRACT

The invention relates to an arrangement for mounting an optical element, in particular in an EUV projection exposure apparatus, comprising a weight force compensation device ( 103 ) for exerting a compensation force on the optical element ( 101 ), wherein said compensation force at least partly compensates for the weight force acting on the optical element ( 101 ), wherein the weight force compensation device ( 103 ) has a passive magnetic circuit for generating a force component of the compensation force acting on the optical element ( 101 ), and wherein at least one adjustment element ( 880 ) is provided by means of which the force component generated by the passive magnetic circuit is continuously adjustable.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of German Patent Applications DE 102010 063 566.9 and DE 10 2010 063 577.4, both filed on Dec. 20, 2010, aswell as U.S. 61/424,823 and U.S. 61/424,855, both also filed on Dec. 20,2010. The content of these applications is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an arrangement for mounting an optical element,in particular in an EUV projection exposure apparatus.

2. Prior Art

Microlithography is used to produce microstructured components such as,for example, integrated circuits or LCDs. The microlithography processis carried out in a so-called projection exposure apparatus having anillumination device and a projection lens. The image of a mask(=reticle) illuminated by means of the illumination device is in thiscase projected by means of the projection lens onto a substrate (e.g. asilicon wafer) coated with a light-sensitive layer (photoresist) andarranged in the image plane of the projection lens, in order to transferthe mask structure to the light-sensitive coating of the substrate.

In a projection exposure apparatus designed for EUV (i.e. forelectromagnetic radiation having a wavelength of less than 15 nm), owingto light-transmissive materials not being present, mirrors are used asoptical components for the imaging process. Said mirrors can be fixede.g. on a carrier frame and can be configured such that they are atleast partly manipulatable, in order to enable a movement of therespective mirror in six degrees of freedom (i.e. with regard todisplacements in the three spatial directions x, y and z and also withregard to rotations R_(x), R_(y) and R_(z) about the correspondingaxes). In this case, it is possible to compensate for changes in theoptical properties that occur for instance during the operation of theprojection exposure apparatus e.g. on account of thermal influences.

WO 2005/026801 A2 discloses, inter alia, using three actuator devices ina projection lens of an EUV projection exposure apparatus for themanipulation of optical elements such as mirrors in up to six degrees offreedom, said actuator devices each having at least two Lorentzactuators and two actively drivable movement axes. Said Lorentzactuators each have two elements which are separated via a gap and oneof which has a solenoid, to which an electric current can be applied inorder to alter the gap, such that the two elements of the Lorentzactuator, of which one is connected to the respective optical element ormirror and the other is connected to the housing of the projection lens,can be moved relative to one another, wherein the two elements of theLorentz actuator are mechanically decoupled on account of the gapsituated between them. Furthermore, a weight force compensation deviceembodied as a spring element, for example, is provided in order tominimize the energy consumption of the active or controllable actuatingelements, since the weight force compensation device substantiallycarries the mass of the optical element or mirror, such that nopermanent energy flow with associated generation of heat is necessary inthis respect. The weight force compensation device (also designated as“MGC”) can be set to a certain holding force that is transmitted to themirror via a mechanical element (pin) that couples mechanically to themirror.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an arrangement formounting an optical element, in particular in an EUV projection exposureapparatus, which enables an improved weight force compensation of theoptical element while also reducing or minimizing the requirement foradditional actuator forces and resulting thermal loads for a positioningof the optical element.

In accordance with one aspect of the present disclosure, an arrangementfor mounting an optical element, in particular in an EUV projectionexposure apparatus, comprises:

-   -   a weight force compensation device for exerting a compensation        force on the optical element, wherein said compensation force at        least partly compensates for the weight force acting on the        optical element;    -   wherein the weight force compensation device has a passive        magnetic circuit for generating a force component of the        compensation force acting on the optical element; and    -   wherein at least one adjustment element is provided by means of        which the force component generated by the passive magnetic        circuit is continuously adjustable.

According to this aspect the invention is based on the concept tocontinuously manipulate, by means of an adjusting element, the magneticfield lines generated by the passive magnetic circuit (which cancomprise for example, as further described in the following, two movableinner magnets and one fixed outer magnet), and thereby to continuouslymanipulate the force component generated by the passive magnetic circuitin order to realize a continuous adjustability of the total resultingcompensation force exerted by the weight force compensation device.

Further advantages which can be achieved using the adjusting elementaccording to the invention comprise a possible reduction of a straymagnetic field as well as an enhancement of the efficiency of anactuator (such as e.g. a Lorentz-Actuator), which can be integrated intothe weight force compensation device according to the present disclosureand as further described below.

According to an embodiment, the adjusting element is axiallydisplaceable relative to the direction of the compensation force,wherein the force component generated by the passive magnetic circuitcan be manipulated by said displacement.

The adjusting element can e.g. (without the invention being restrictedthereto) be made of a soft-magnetic material. A soft-magnetic materialdenotes, here and in the following, a material which has a coercivefield strength of less than 1000 A/m. Any suitable soft-magneticmaterials can be used, such as e.g. iron (Fe), cobalt (Co) or Nickel(Ni), or alloys of the before-mentioned or other materials.

According to an embodiment the adjustment element can comprise at leastone permanent magnet. In further embodiments, the adjustment elementcomprises at least one coil to which an electric current can be applied.By means of such a current-carrying coil, the magnetic properties of thepassive magnetic circuit can be manipulated. Such a coil can be used, ifcarrying an electric direct current, to generate a constant magneticfield that is superimposed on the magnetic field generated by thepassive magnetic circuit. Furthermore, such a coil can be used, by meansof impulse-like current-application with of relatively short duration(e.g. with pulse duration of less than 1 ms) with a relatively largeelectric current (e.g. larger than 50 A), in order to permanently modifythe magnetic properties (in particular the remanence magnetisation) ofthe passive magnetic circuit, which effects the total compensation forceexerted by the weight force compensation device on the optical element.

According to an embodiment the adjustment element at least partlysurrounds the weight force compensation device.

The invention is, however, in no way restricted to a certain geometry ofthe adjustment element. According to an embodiment, the adjustmentelement can e.g. have a ring-shaped geometry. The adjustment element canalso have, dependent on the specific arrangement used, also any othergeometry (which can be rotational symmetric or non-rotationalsymmetric). In general, all embodiments are comprised by the presentinvention in which a force generated by the passive magnetic circuit canbe continuously manipulated by means of at least one adjustment element,wherein the adjustment element can be embodied in any suitable componentshape, e.g. with a plate-like, axle-like or screw-like shape.Furthermore, the adjustment element can also partly overlap the passivemagnetic circuit.

By means of selecting a specific embodiment of the adjustment element,e.g. with respect to an asymmetric arrangement of the adjustmentelement, the position and the size and geometric dimensions of theadjustment element, the magnetic properties of the passive magneticcircuit can be systematically affected, e.g. in order to at least partlycompensate impacts (e.g. by means of a magnetic shunt) possibleparasitic effects such as e.g. non-desired magnetic circuit effects dueto mechanical tolerances and transverse forces as well as massvariations of an optical element the weight force of which is to becompensated and/or non-desired thermal.

Furthermore, a linearization of the so-called adjustment setting curve(describing the dependency of the force exerted by the weight forcecompensation device on the position of the adjustment element) as wellas a reduction of the “stiffness” of the weight force compensationdevice or a reduced force variance can be achieved by an appropriatedesign of the (e.g. soft-magnetic) adjustment element.

The adjustment element can (without the disclosure being restrictedthereto) e.g. be a component of the weight force compensation device. Infurther embodiments, the adjustment element can also be integrated intoa housing surrounding or encompassing the weight force compensationdevice. The adjustment element can, in particular, be integrated into aforce frame of an EUV-projection objective. Such embodiments areadvantageous with respect to an easy accessibility of the adjustmentelement, e.g. in order to select its position or with respect to heatdissipation.

The adjustment or positioning, respectively, of the adjustment elementcan be performed manually or in a (preferably self-locking) motorizedoperation, wherein the position of the adjustment element isselected/adjusted by means of an appropriate position actuator.

According to an embodiment, the arrangement further comprises a controlsystem, wherein a position of the adjustment element can be controlledby said control system. This can be done e.g. in dependence on at leastone operation parameter of the arrangement. This operation parameter cane.g. be the position of the optical element, the force acting on theoptical element or the magnetic field strength. Here, atemperature-induced or ageing-induced change of the compensation forceexerted by the weight force compensation device on the optical elementis reduced compared to an analogous arrangement without the controlsystem.

In accordance with a further aspect present disclosure also relates toan arrangement for mounting an optical element, in particular in an EUVprojection exposure apparatus, comprising:

-   -   a weight force compensation device for exerting a compensation        force on the optical element, wherein said compensation force at        least partly compensates for the weight force acting on the        optical element; and    -   at least two actuators which each exert a controllable force on        the optical element;    -   wherein at least one of the actuators generates the controllable        force on the optical element in the direction of the        compensation force.

This aspect is based on the concept, in particular, in contrast to theconstruction explained in the introduction, in the direction of thecompensation force exerted on the optical element, of additionally alsoexerting an actively controllable force on the optical element, that isto say in other words of realizing the axis along which the compensationforce for the compensation of the weight force acting on the opticalelement is generated as an actively drivable movement axis of theoptical element.

By virtue of the fact that one of the actuators generates thecontrollable force on the optical element in the direction of thecompensation force, firstly it is possible to obtain a significantreduction of the required structural space.

In accordance with the disclosure, the weight force compensation devicecan, in particular, itself be embodied as an actuator. In this case,therefore, the weight force compensation device is no longer designedonly passively for generating a compensation force that is set once andthen maintained substantially in constant fashion, but rather realizes adouble function insofar as it firstly continues to ensure the weightcompensation and secondly is able to generate a controllable (active)force. In this case, in particular, one of the two Lorentz actuatorsconventionally provided (also designated as “voice coil motor” or “VCM”)can be integrated into the weight force compensation device.

In this case, the disclosure is not restricted to the direct integrationof a Lorentz actuator into the weight force compensation device. Infurther embodiments, it is also possible to configure the Lorentzactuator and the weight force compensation device as separate functionalunits, for instance by virtue of the fact that the Lorentz actuatoracting in the direction of the compensation force is arranged separatelyfrom or outside the weight force compensation device, but neverthelessgenerates its drive force in the same force direction in which thecompensation force generated by the weight force compensation devicealso acts.

In accordance with one embodiment, a passive magnetic circuit isprovided for generating the force acting oppositely to the weight force.This has the advantage that on the part of the active portion acomparatively low actuation force is required and, consequently, thethermal loads and parasitic effects associated with the force changesgenerated can be kept small.

In accordance with a further embodiment, it is also possible, whilstcompletely dispensing with a passive magnetic circuit (such as iscontained in the conventional weight force compensation device explainedin the introduction), for generating a force acting oppositely to theweight force, to use only a single Lorentz actuator, which is designedto be sufficiently strong and which is able not only to generate acontrollable force on the mirror but at the same time to generate theforce necessary for compensating for the mirror weight and thussimultaneously performs the function of the weight force compensationdevice.

In accordance with one embodiment, the actuator acting in the directionof the compensation force, or the weight force compensation device, hasat least one coil to which an electric current can be applied and whichserves for generating a controllable magnetic force transmitted to theoptical element via at least one movable actuator element.

The coils can be arranged, in particular, in the stationary part of theactuator acting in the direction of the compensation force. This firstlyhas the advantage that thermal loads proceeding from the coils can bedissipated toward the outside in a simple manner, and that it is notnecessary to realize any cable feeds to the movable part. However, thedisclosure is not restricted thereto. Rather, the coils, in a furtherembodiment, can also be arranged in the moved part of the actuatoracting in the direction of the compensation force. By means of such aconfiguration, the mass present in the moved part can be reduced sincethe coils are typically lighter than the magnets forming the respectiveother actuator component.

In accordance with one embodiment, the movable actuator component, i.e.the magnet(s) to which the Lorentz force is applied by the coils of theactuator through which current flows, is provided by magnets alreadypresent (anyway) in the passive magnetic circuit. Consequently, noadditional permanent magnets over and above the passive magnetic circuitare required for the construction of the actuator, which leads, inparticular, to a greater compactness of the system.

In accordance with one embodiment, the optical element is a mirror.

In accordance with one embodiment, a mechanical coupling is formedbetween at least one of the actuators and the optical element in amanner such that, relative to the drive axis of said actuator, the ratioof the stiffness of said mechanical coupling in an axial direction tothe stiffness in a lateral direction is at least 100.

In accordance with one embodiment, for said mechanical coupling, thenatural frequency in an axial direction is at least 3 times thebandwidth of the regulation.

In accordance with one embodiment, for said mechanical coupling, thenatural frequency in an axial direction is in the range of 600 Hz to1800 Hz, in particular in the range of 800 Hz to 1400 Hz, moreparticularly in the range of 1000 Hz to 1200 Hz.

The realization of the above natural frequencies and the low-passfiltering that can be obtained therewith in the case of the mechanicalcoupling is not restricted to the above-described concept (i.e. thegeneration of the controllable force by at least one actuator in thedirection of a compensation force exerted by a weight force compensationdevice) or to the presence of a weight force compensation device at all,but rather is also advantageous independently thereof.

In accordance with a further aspect, therefore, the disclosure alsorelates to an arrangement for mounting an optical element, in particularin an EUV projection exposure apparatus, comprising

-   -   at least two actuators which each exert a controllable force on        the optical element;    -   wherein a mechanical coupling is formed between at least one of        the actuators and the optical element in a manner such that,        relative to the drive axis of said actuator, the ratio of the        stiffness of said mechanical coupling in an axial direction to        the stiffness in a lateral direction is at least 100.

In accordance with a further aspect, the disclosure also relates to anarrangement for mounting an optical element, in particular in an EUVprojection exposure apparatus, comprising:

-   -   at least two actuators which each exert a controllable force on        the optical element;    -   wherein, for said mechanical coupling, the natural frequency in        an axial direction is in the range of 600 Hz to 1800 Hz, in        particular in the range of 800 Hz to 1400 Hz, more particularly        in the range of 1000 Hz to 1200 Hz.

In accordance with one embodiment, the mechanical coupling has a pinprovided with two universal joints. In this case, a universal jointshould be understood, within the meaning of the present application, tobe a joint which has two tilting joints with orthogonal orientation ofthe tilting axes with respect to one another (or tilting jointsconnected in series relative to the force flux), which preferably have acommon pivot point.

In accordance with one embodiment, the pin has a first partial element,in which one of the two universal joints is formed, and also a secondpartial element, which is connected to the first partial element in areleasable manner and in which the other of the two universal joints isformed.

In accordance with a further aspect, the invention provides anarrangement for mounting an optical element in an optical system, inparticular in an EUV projection exposure apparatus, comprising

-   -   a weight force compensation device for exerting a compensation        force on the optical element, wherein said compensation force at        least partly compensates for the weight force acting on the        optical element;    -   wherein the weight force compensation device has at least one        magnet which is movable relative to a stationary frame of the        optical system and at least one magnet which is stationary        relative to said frame; and    -   wherein the at least one magnet which is movable relative to the        frame is mounted in movable fashion in a direction that deviates        from the direction of the compensation force.

In accordance with one embodiment, the weight force compensation deviceis mechanically coupled to the optical element by means of a pin.

In accordance with one embodiment, the at least one magnet which ismovable relative to the frame is mounted in movable fashion in adirection non-parallel to the longitudinal axis of the pin.

In accordance with one embodiment, a deflection of the pin in adirection that deviates from the direction of the compensation forceleads to a relative movement between the magnet which is movablerelative to the frame and the magnet which is stationary relative to theframe.

In accordance with one embodiment, said relative movement generates amagnetic moment which at least partly compensates for a transverse forceacting on the pin in a direction that deviates from the direction of thecompensation force.

In accordance with one embodiment, a mechanical coupling is providedbetween the frame and the magnet which is movable relative to the frame,said mechanical coupling enabling both an axial displacement of themagnet which is movable relative to the frame in the direction of theweight force and a tilting of the magnet which is movable relative tothe frame about a rotational axis perpendicular to the direction of theweight force.

In accordance with one embodiment, said mechanical coupling has an axialguide and a rotary joint.

In accordance with one embodiment, the axial guide is formed by aparallel spring system composed of two leaf springs.

In accordance with one embodiment, said mechanical coupling has a springelement, which enables both an axial displacement of the magnet which ismovable relative to the frame in the direction of the weight force and atilting of the magnet which is movable relative to the frame about atleast one rotational axis perpendicular to the direction of the weightforce.

In accordance with one embodiment, the mechanical coupling formed bysaid spring element has a natural frequency in the axial direction inthe range of 600 Hz to 1800 Hz, in particular in the range of 800 Hz to1400 Hz, more particularly in the range of 1000 Hz to 1200 Hz.

In accordance with one embodiment, the pin has two universal joints.

In accordance with one embodiment, the optical element is a mirror.

Further configurations of the invention can be gathered from thedescription and also the dependent claims.

The invention is explained in greater detail below on the basis ofexemplary embodiments illustrated in the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures:

FIG. 1 shows a basic schematic diagram for elucidating the conceptunderlying the invention;

FIGS. 2-3 show schematic illustrations for elucidating one possibleembodiment for realizing the concept from FIG. 1;

FIG. 4 shows a basic schematic diagram for elucidating a furtherembodiment of the invention;

FIGS. 5 a-6 b show schematic illustrations of possible embodiments ofleaf springs used in the construction from FIG. 2;

FIG. 7 shows a diagram elucidating, on the basis of force-distancecharacteristic curves, the method of operation of the leaf springs shownin FIGS. 5 a, 5 b and 6 a, 6 b;

FIG. 8 shows a schematic illustration for elucidating a further possibleembodiment of the construction from FIG. 2 using an adjustment ring;

FIGS. 9-10 show schematic illustrations for elucidating the method ofoperation of a hollow joint used in one embodiment of the invention inthe construction from FIG. 2; and

FIGS. 11-12 a-12 b-13 a-13 b-14 show schematic illustrations forelucidating a further aspect of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 firstly shows a basic schematic diagram for elucidating a conceptunderlying the disclosure.

As is illustrated merely schematically, both a Lorentz actuator 102,which applies an actively controllable force, and a weight forcecompensation device 103 act on an optical element such as e.g. a mirror101. In contrast to the construction known from WO 2005/026801 A2, asexplained in the introduction, now in the direction of the compensationforce exerted on the mirror 101 by the weight force compensation device103, an actively controllable force is additionally exerted on themirror 101. This is symbolized in FIG. 1 by a Lorentz actuator (=VCM)additionally being integrated into the weight force compensation device103. Consequently, the weight force compensation device 103, which willbe described in greater detail below, performs a double function insofaras it firstly continues to ensure the weight compensation and secondlyis able to generate a controllable (active) force on the mirror 101.

In the context of the present application, the drive direction of anactuator is in each case defined as the z-direction, whereas the x-yplane runs perpendicular to said drive direction. Consequently, in FIG.1 and also in the further figures, a dedicated coordinate system is ineach case assigned to the respective actuators.

Reference is made below to the sectional view from FIG. 2 for moredetailed elucidation of one embodiment of the disclosure.

In this case in accordance with FIG. 2, in particular in a departurefrom the concept realized e.g. in WO 2005/026801 A2, one of the Lorentzactuators that act in a manner deviating from the weight force directionor are provided in addition to the weight force compensation device isdispensed with by virtue of the weight force compensation device 103itself being embodied as an actuator. Consequently, only one lateralLorentz actuator 102 remains, which in the exemplary embodiment (withoutthe disclosure being restricted thereto) is arranged at an angle of 60°with respect to the vertical. In accordance with this exemplaryembodiment, therefore, the weight force compensation device 103 (whichconventionally acts only passively) is extended to the effect that anactive manipulated variable can be applied, such that now, therefore, acombined movement axis that acts actively and also passively at the sametime exists, which is advantageous firstly for reasons of structuralspace, in particular.

The weight force compensation device 103 from FIG. 2 is therefore nolonger designed only passively, but rather performs a double function byvirtue of the fact that it firstly continues to ensure the weightcompensation and secondly one of the two Lorentz actuatorsconventionally provided is integrated into the weight force compensationdevice, such that the weight force compensation device is simultaneouslyable to generate a controllable (active) force.

“220” schematically indicates a linear guide (or axial guide) which, inthe exemplary embodiment, is configured as a parallel spring systemcomposed of specifically designed leaf springs (which will be explainedin even greater detail further below with reference to FIGS. 5 a, 5 b, 6a and 6 b), which substantially have the function of obtaining a linearguide which is free with regard to displacement in the z-direction androtation about the z-axis.

Furthermore, in accordance with FIG. 2, a pin 210 extending in thevertical direction or running axially relative to the drive direction orz-direction is present, which transmits the movement in the verticaldirection to the mirror 101 and has two universal joints 211, 212 orcardan joints, such that the pin 210 transmits a force or movement onlyin the axial direction, whereas substantial decoupling is present in allthe other directions, as will be explained in even greater detail below.

The magnetic circuit itself comprises, as illustrated in even greaterdetail with reference to FIG. 8, firstly conventionally a passivemagnetic circuit composed of an outer magnetic ring 233, which, in theexemplary embodiment illustrated, is polarized radially relative to thez-axis running in the drive direction, and also two magnetic rings 231,232 arranged radially further inward, which, in the exemplary embodimentillustrated, are in each case polarized axially relative to the z-axis,wherein both the outer magnetic ring 233 and the magnetic rings 231, 232arranged in an inner position are in each case embodied as permanentmagnets. This inner assembly is guided by means of the linear guideformed by the parallel spring system 220 composed of leaf springs.

The disclosure is not restricted to the illustrated magnetizationdirections and embodiments of the magnetic rings, which can be realizedin many other variants (e.g. as described in WO 2009/093907 A1).

The passive magnetic circuit generates, in a manner known per se, aforce which acts in a vertical direction and which is intended tocompensate for the weight force. The two magnetic rings 231, 232arranged radially in an inner position are displaceable in the verticaldirection (i.e. vertically displaceable), as a result of which they canbe positioned variably both with respect to one another and relative tothe radially outer magnet 233, wherein the force that can ultimately betransmitted via the passive magnetic circuit formed by the magneticrings 231-233 can be set by varying these positions of the magneticrings 231, 232. More precisely, variation of the axial spacing of theinner magnetic rings 231, 232 primarily determines the magnitude of theforce which is exerted by the magnetic field on the movable innerassembly with the moved mass carrying the mirror 201, and thedisplacement of the inner magnetic rings 231, 232 with respect to theouter magnetic ring 233 primarily determines the position of the forcemaximum of the actuator characteristic curve relative to the mechanicalposition of the carrier frame.

By means of the axial distance between the radially inner magnetic rings231, 232, therefore, a fixed force value can be set by means of thepassive magnetic circuit, wherein the setting and designing of theweight force compensation system are optimally effected in terms of thedesign such that no or only a minimal force change (dominated by thedesign of the magnetic circuit) occurs via the movement typicallyperformed by the mirror 201.

In contrast to the conventional construction realized in WO 2005/026801A2, for example, two coils 241, 242 are now provided in the exemplaryembodiment, wherein, by means of applying an electric current to thecoils 241, 242 according to the principle of the Lorentz actuator, acontrollable force acting in the vertical direction can be exerted onthe moved inner part. Even though the exemplary embodiment shows twocoils, in further embodiments in this respect it is also possible toprovide more or fewer coils, i.e. in particular also only a single coil.

The coils 241, 242 act on the two axially polarized magnetic rings 231,232 which are arranged radially in an inner position and are movable inthe vertical direction by means of the linear guide formed by the leafsprings. In other words, by applying an electric current to the coils241, 242, a Lorentz force is generated and an increase or decrease inthe generated force is thus achieved. While solely the arrangementcomposed of radially inner magnets 231, 232 forms a passive magneticcircuit, the additional arrangement of the coils 241, 242 turns theentire arrangement composed of the coils 241, 242, the radially innermagnets 231, 232 and the radially outer magnet 233 into an activelycontrollable magnetic circuit by means of which an actively controllableforce can be transmitted to the mirror 101.

Even though, in the exemplary embodiment from FIG. 2, the coils 241, 242to which an electric current can be applied or the actuator formed bysaid coils is integrated into the weight force compensation device, thedisclosure is not restricted thereto. Rather, in further embodiments, itis also possible to provide the Lorentz actuator and the weight forcecompensation device as separate functional units, for instance by virtueof the Lorentz actuator or voice coil drive together with its functionalunits of coil and passive magnets being arranged outside (e.g. in FIG. 2below) the weight force compensation device.

FIG. 3 shows a schematic illustration for elucidating a dynamic modelunderlying the arrangement from FIG. 2, wherein, in particular, theuniversal joints 211, 212 and 251, 252 of the pins 201 and respectively250, on the one hand, and the parallel spring systems 220 andrespectively 260, on the other hand, are represented by spring symbolswith associated joint points (symbolized by the open circles).

As far as in this illustration firstly the Lorentz actuator (=VCM) 102is concerned, this Lorentz actuator not acting in the weight forcedirection, in accordance with the right-hand part of FIG. 3 MPin_(VCM)designates the mass of the pin 210, which couples the mirror 201 to thepermanent magnet 272 of the Lorentz actuator 102 via the springconnections formed by the universal joints 211, 212 (the fixed linkingbeing symbolized by the closed circle). For its part, the moved massm(VCM) of the permanent magnet is coupled via the parallel spring system260, which is symbolized by springs with associated joint points, to thecoil 271 of the Lorentz actuator 102, said coil being connected to thestationary surroundings.

Analogously, as far as the weight force compensation device 103 isconcerned, MPin_(MGC) designates the mass of the pin 250, which, via thespring connections formed by the universal joints 251, 252, couples themirror 201 to the moved mass—designated by m(MGC)—of the weight forcecompensation device 103 (in particular the magnetic rings 231, 232arranged radially in an inner position from FIG. 2). For its part, saidmoved mass of the weight force compensation device 103 is coupled viathe parallel spring system 220, which is likewise symbolized by springswith associated joint points, to the components of the weight forcecompensation device 103 (in particular coils 241, 242 and radially outermagnetic ring 233) which are connected to the stationary surroundings.

In a further exemplary embodiment illustrated schematically in FIG. 4,it is also possible to provide two drives 404, 405 each firstly actingpassively in the manner of the conventional weight force compensationdevice and to supplement them in each case by an active component (i.e.in the manner of the coils 241, 242 from FIG. 2). Consequently, the twopassive-active drives 404 and 405 from FIG. 4 have in each case bothcoils to which electric current can be applied and a permanent magneticcircuit which inherently acts passively. These two drives 404 and 405are arranged (e.g. at in each case 45° with respect to the vertical)precisely in such a way that in the “original state” in total the forceeffect of the passive magnetic circuits arises for weight forcecompensation in the vertical direction and (virtually) no horizontalforce effect remains.

In yet another exemplary embodiment, the weight force compensationdevice from FIG. 2 can also be designed such that, while dispensing witha passively acting drive, it comprises only an active system. In thisexample, therefore, the overall system has two Lorentz actuators oractive drives, one of which acts along the vertical and thussimultaneously performs the function of the weight force compensationdevice.

The construction of the Lorentz actuator 102 (i.e. of the Lorentzactuator not integrated into the weight force compensation device) inaccordance with one embodiment is explained in greater detail below.

The construction of the Lorentz actuator 102 from FIG. 2 includes afurther departure from the conventional concept (realized e.g. in WO2005/026801 A2) of fitting the Lorentz actuators by their respectivepassive part (i.e. the movable permanent magnet) fixedly in the sense ofa rigid-body connection to the mirror.

In the concept described here, as explained in further detail below, bymeans of a pin 250 that is designed in a suitable manner and bringsabout a partial “decoupling” explained below, there is a mechanicalconnection to the movable part or permanent magnet of the Lorentzactuator, which in turn, for its part, is guided linearly.

More precisely, in the construction from FIG. 2—in contrast to theconventional construction—a specific pin 250 with cardan joints and leafsprings are additionally provided, the configuration of which isexplained in greater detail below. In the exemplary embodiment, the pin250 in the same way as the remaining parts with the exception of theradially inner or the radially outer magnetic rings is produced from amaterial that is non-magnetic in order to avoid an undesirableinfluencing of the magnetic fields generated, wherein in particulartitanium is suitable for the pin 250 and e.g. high-grade steel is alsosuitable for the remaining (carrier) parts.

In further embodiments, it is also possible to use additional “returnpath elements” composed of magnetically highly permeable material forflux guidance and reduction of losses and leakage fields.

The pin 250 has for the purposes of decoupling in the lateral direction(i.e. perpendicularly to the drive axis) in its respective end sectionstwo universal joints or cardan joints 251, 252, with the result that ithas a high degree of stiffness only in the axial direction fortransmitting a force or movement, whereas only a low degree of stiffness(i.e. a decoupling) is present in all other directions.

The departure from the conventional concept of a rigid-body connectionbetween permanent magnet of the Lorentz actuator, on the one hand, andmirror, on the other hand, takes account of the fact that saidrigid-body connection, on account of the significant mass coupling, canresult in a reduction of the natural frequency of the overall system anda generation of dynamic modes that are undesirable or controllable onlywith difficulty. That is based on the consideration that every mirrorpresent in the system has, as an oscillatory body, fundamentaleigenmodes or intrinsic stiffnesses which, depending on the massescoupled to the mirror, are influenced undesirably to the effect thatthey firstly decrease in relation to low frequency values (i.e.eigenmodes other than the fundamental eigenmodes of the mirror aregenerated) and secondly assume high amplitudes. With regard to the factthat the accuracies of the positionings of the mirror surfaces that areto be performed typically lie in the picometers range, the changesconcerned in the eigenmodes or intrinsic stiffnesses can become sorelevant that they can no longer be combated by control engineering. If,by way of example, a typically required control bandwidth (determined bythe natural frequencies of controlled system and controller) of at least100 Hz is taken as a basis, within which the system has to becontrollable or able to be supervised, then the above-described decreasein the natural frequencies can have the effect that, owing to thedecrease in the natural frequencies of the controlled system, the systemcan no longer be brought to the desired control bandwidth by thecontroller.

In order to take account of that, in the form of the pin provided withuniversal joints, mechanical elements are used for linking the Lorentzactuators to the mirrors, by means of which the sum of the mechanicalelements has a comparatively high natural frequency in the drivedirection, on the one hand, but has suitable compliances in the otherdegrees of freedom. In other words, the stiffness set for the pin 250 inthe axial (drive) direction or z-direction is comparatively high,whereas the pin 250 has extremely soft behavior in the other directionssince the universal joints 251, 252 have only very low stiffnesstransversely with respect to the drive direction or z-direction.

In other words, the coupling of the passive or movable part of theLorentz actuator 102 to the mirror 201 is realized as a mass-springoscillator which can be determined well or can be designed in a definedmanner in terms of its dynamic properties or its stiffness and thenatural frequency f of which is linked to the stiffness k (in units ofN/m) by means of the relationship:

$\begin{matrix}{f = {\frac{1}{2 \cdot \pi}\sqrt{\frac{k}{m}}}} & (1)\end{matrix}$

where m denotes the mass coupled via the spring.

Generally, the natural frequency should be at least three times therequired bandwidth of the control.

In the specific exemplary embodiment, said natural frequency is 1200 Hzin the z-direction. In this case, excitations whose frequency exceeds1200 Hz are coupled into the mirror 201 only with great attenuation,since the system composed of moved mass formed by the permanent magnet272 and spring realized by the pin 250 brings about a correspondinglow-pass filtering. The natural frequencies should in each case bechosen suitably in a manner dependent on the specific controllerconcept. Preferably, the natural frequency in the axial direction is inthe range of at least 600 Hz, in particular at least 800 Hz, and belowapproximately 1800 Hz, in particular in the range of 800 Hz to 1400 Hz,more particularly in the range of approximately 1000 Hz to 1200 Hz.Furthermore, the ratio of the natural frequencies in the lateraldirection and axial direction is preferably at least 1:100.Correspondingly, on account of the relationship from equation (1),therefore, the ratio of the stiffnesses in the lateral direction andaxial direction is at least 1:10000.

The mechanical connection—furthermore required for force transmission—ofthe Lorentz actuator 102 or of the moved part thereof to the mirror 101is thus designed specifically with respect to a natural frequency of thecoupled system. While in the case of the conventional rigid linking tothe mirror, as explained above, the masses concomitantly moving togetherwith the mirror cannot oscillate independently, in the presentdisclosure the moved mass (i.e. the permanent magnet 272) of the Lorentzactuator 102 is dynamically linked to the mirror 201 via the pin 250,with the result that the natural frequency in the axial (drive)direction is determined by the coupled mass and the specificallydesigned stiffnesses of the pin 250.

The stiffnesses present in the lateral directions are preferably notrealized solely by means of the singular system of the spring-massoscillator that produces the coupling of the passive or movable part ofthe Lorentz actuator 102 to the mirror 201, but rather by means ofadditional spring elements provided for lateral support. These springelements are designed such that the movable part of the Lorentz actuator102 (i.e. the permanent magnet 272) substantially only performs a linearmovement relative to the stationary coil 271, that is to say that thepin 250 is guided only along one axis with low stiffness, acorrespondingly high stiffness being present in all other directions. Aswill be explained below with reference to FIGS. 5 a, 5 b, 6 a and 6 b,in embodiments of the disclosure a parallel spring system 260 composedof specifically designed leaf springs which bring about an additionaltorsional decoupling is used for this purpose. Said leafsprings—oppositely to the pin 250—are relatively soft in the axialdirection and significantly influence the stiffness only in the lateraldirection.

In the context of the disclosure, therefore, the movable part orpermanent magnet 272 of the Lorentz actuator 102 is mechanically coupledto the stationary part of the Lorentz actuator 102, said stationary parthaving the coil 271 through which current flows. On account of thiscancellation of the above-described conventional decoupling betweenmovable permanent magnet 272 and stationary coil 271, it is furthermoreof particular importance, by means of corresponding embodiment of theparallel guide of the movable part or permanent magnet, for possibleparasitic forces or parasitic moments which are transmitted to themirror 101 via the mechanical coupling or spring joints to be kept in arange that can still be afforded tolerance, which is effected by meansof the parallel spring system comprising leaf springs that will beexplained below.

Overall, therefore, in the construction from FIG. 2, the Lorentzactuator 102 is mechanically coupled to the overall system in all sixdegrees of freedom with a specifically adjustable stiffness, whereinthis coupling is effected with the passive part (moved mass or permanentmagnet 272) of the Lorentz actuator 102 via the spring effect of the pin250 to the mirror 201 and simultaneously to the rest of the surroundingsvia the parallel spring system 260.

Embodiments of the parallel spring system 260 composed of leaf springs,as already mentioned, will be explained below with reference to FIGS. 5a, 5 b, 6 a and 6 b. This parallel spring system 260 is used since, bymeans of the design of the pin 250, although it is possible to set thedesired natural frequency for the degree of freedom of the displacementin the z-direction (i.e. in the axial direction along the drive axis)(e.g. to the above-mentioned exemplary value of 1200 Hz), the pin 250alone does not yet produce natural frequencies that can be determinedfar enough or in a targeted manner in the lateral direction (i.e. in thex-y plane perpendicular to the drive axis). In particular, for instancethe stiffness with respect to the degree of freedom of the rotationabout the z-axis (i.e. R_(z)) substantially arises as a parasitic,non-controllable disturbance variable from the set natural frequencywith respect to the degree of freedom of the displacement in thez-direction.

The function of the parallel spring system 260 or of the leaf springelements described below is firstly a guide in the desired operative ordrive direction (i.e. in the z-direction) and secondly a support in thelateral direction (i.e. in the x-y plane).

The configuration of the leaf spring 500 already mentioned above inaccordance with one embodiment is explained below with reference toFIGS. 5 a and 5 b. In this case, use is made of a construction composedof two leaf springs 500, which are arranged in a manner connected inseries along the operative direction of the Lorentz actuator 102 andjointly permit substantially only a linear movement in the drivedirection or z-direction.

The movable pin 210 coupled to the mirror 101 is fixedly connected tothe radially inner section of the leaf spring 500, whereas thestationary surroundings are fixedly connected to the radially outersection of the leaf spring 500. In accordance with FIGS. 5 a and 5 b,the leaf spring 500 has three bending beams 510, 520 and 530 arrangedtangentially. FIGS. 6 a and 6 b show one advantageous furtherdevelopment of a leaf spring 600, likewise having three bending beams610, 620 and 630 arranged tangentially.

The tangential arrangement of the bending beams 610, 620 and 630 bringsabout, in the case of an axial deflection, in addition to the desiredz-displacement, a parasitic rotary movement which results from thedeflections of the three bending beams 610, 620 and 630 and, givenidentically oriented installation of the leaf springs 600, leads to astrain of the pin 210 and a force on the mirror 101. Given torsionallystiff arrangement of the leaf spring 600, a rotary movement leads to anadditional strain of the bending beams 610, 620 and 630 and thus to agreat increase in the axial stiffnesses. If two leaf springs 600 thatare installed in opposite directions or act against one another areused, the leaf springs 600 are tensioned against one another, which,upon deflection of the leaf springs 600, results in an increase in thespring force such that the leaf springs 600 exhibit stiffer behaviorwith increasing deflection.

The above-described effect of the parasitic rotary movement can bewholly or partly reduced in the embodiment from FIGS. 5 a and 5 b by thedouble or bent guidance of the individual bending beams 510, 520 and 530running back and forth. In the exemplary embodiment from FIGS. 6 a and 6b, by contrast, three leaf spring decoupling joints extending radiallyoutward are additionally present. Each of said leaf spring decouplingjoints has in each case a bending beam 615, 625 and 635, respectively,which runs in the radial direction and which forms in each case adecoupling web for connection between the radially inner section and theradially outer section, with the result that the radially inner sectionof the leaf spring 600 can be rotated relative to the radially outersection of the leaf spring 600. The decoupling joints which bring aboutthe torsional decoupling can be arranged radially on the inner side orelse radially on the outer side with respect to the bending beams.

The decoupling joints described above can bring about an additionaltorsional decoupling with respect to the above-described rotary movementinduced by an axial deflection. The bending beams 615, 625 and 635running in the radial direction are embodied only with a relativelysmall thickness in the tangential direction or in the x-y plane and aretherefore relatively soft (that is to say have a good compliance withrespect to rotation about the z-direction, i.e. with respect to thedegree of freedom R_(z)), but in the z-direction are relatively thick(e.g. of the order of magnitude of 0.3-2.5 mm) and thus relativelystiff. As a result, what is also achieved thereby is that the leafspring 600 becomes less sensitive to introduced torsional stressesduring assembly, horizontal stiffnesses being impaired only minimally.

In other words, the respective stiffnesses (in units of N/m) should beconstituted such that the aspect ratio between the lateral stiffness(i.e. the stiffnesses with respect to displacements in the x-y plane,which correspond on account of the rotational symmetry) and the axialstiffness (i.e. the stiffness for displacement in the direction of thez-axis) is as high as possible. In the ideal case, the leaf springswould result in a complete fixing in the x-y plane and a linear guide(without any stiffness) in the z-direction, i.e. the desired operativedirection. Quantitatively, the ratio between lateral stiffnesses andaxial stiffness is at least 3000, in particular at least 6000, moreparticularly at least 9000.

Furthermore, preferably, on account of the leaf spring decoupling jointsdescribed above, the maximum actuating force occurring over the entiretravel of the leaf springs 600 is smaller by a factor of two than in ananalogous construction without the additional radial decoupling elementsor webs: on account of the configuration of the leaf springs, theforce/distance characteristic curve illustrated in the diagram in FIG. 7now acquires a flatter profile. What is sought is a spring stiffnessthat is as constant as possible (corresponding to a constant gradient ofthe force-distance characteristic curve over the entire travel x),wherein, moreover, said gradient or the spring stiffness should have avalue that is as low as possible. In FIG. 7, curve “A” shows anexemplary characteristic obtained for two leaf springs installed inopposite directions without the torsional decoupling described withreference to FIGS. 6 a and 6 b, and curve “B” shows the correspondingcharacteristic with the torsional decoupling described with reference toFIGS. 6 a and 6 b. The improvement obtained with curve “B” is manifestedprimarily in the case of higher deflections (i.e. larger travel).

Even though, in the exemplary embodiment from FIG. 2, the leaf springsdescribed with reference to FIGS. 6 a and 6 b are used only in theweight force compensation device 103, they can, in principle, also beprovided in the region of the Lorentz actuator 102 that does not act inthe z-direction.

As already described on the basis of the construction in FIG. 2, inprinciple the setting of the passive force component in the verticaldirection can be effected by varying the position of the radially innermagnets 231, 232 relative to one another and/or relative to the outermagnet 233.

According to FIG. 8 an additional adjustment element 880 (which is, inthe embodiment of FIG. 8, an adjustment ring) is used in order tocontinuously adjust the total compensation force exerted by the weightforce compensation device 103 by means of a continuous manipulation ofthe force component generated by the passive magnetic circuit. In theembodiment (but without the invention being restricted thereto) theadjustment element 880 has a ring-shaped geometry and is made of asoft-magnetic material. By means of a displacement of the adjustmentelement 880 in the vertical direction (i.e. in an axial directionrelative to the direction of the compensation force exerted by theweight force compensation device) the magnetic field lines generated bythe passive magnetic circuit (formed by the radially inner magneticrings 831, 832 and the radially outer magnetic ring 833), and therebythe force which is finally exerted on the optical element or the mirror,respectively, can be continuously and reversibly manipulated.

The arrangement of this adjustment ring 880 has the advantage that, onaccount of the fact that even a displacement of this ring over arelatively large distance brings about only a relatively small change(typically by a few percent, e.g. 1-2%) in the force generated by thepassive magnetic circuit, it is possible to perform a fine adjustmentwhich, firstly, is more difficult to realize by means of the passivemagnetic circuit itself and, secondly, also does not require directaccess to the passive magnetic circuit itself.

During operation, therefore, firstly (for a preliminary or coarseadjustment) the magnetic field is preset by means of the distancesetting of the inner magnetic rings 831, 832 and is subsequently variedby means of the adjustment ring 880 still in a small setting range (of afew percent), by virtue of the adjustment ring 880 exerting, dependingon the specific requirements, an attenuating or amplifying effect on themagnetic field and hence on the force transmitted to the mirror 101. Theadjustment by means of the outer adjustment ring 880 has the furtheradvantage that a heat input into the system which would accompany a finesetting—likewise possible in principle—by means of the coils (notillustrated in FIG. 8) as active part of the device can be avoided inthis respect.

In further embodiments, it is also possible to use two adjustmentelements or adjustment rings, respectively, which can be arranged, inparticular, symmetrically with respect to the central plane of the outermagnetic ring. Furthermore, in even further embodiments, it is alsopossible to use more than two adjustment elements or adjustment rings,respectively, which can be arranged in serious with one another.

The construction of the bush joint already mentioned in accordance withone preferred embodiment is explained below with reference to FIGS. 9and 10. The pin 210 firstly has, in a manner known to this extent, twocardan joints 211, 212, by means of which a decoupling in the directionsnot extending axially is obtained.

Furthermore the pin 210 is configured in a particular manner such thatit has a first partial section, in which one of the two universal joints211 is arranged, and also a second partial section, which is separatefrom the first partial section or arranged via a mechanical interfaceand in which the other of the two universal joints 212 is arranged(instead of the pin 210 being embodied integrally or monolithically).Furthermore, in one preferred configuration, one of the cardan joints212 is embodied as hollow on the inside, such that the pin 250 can beled through this cardan joint 252 and a freely selectable force flux canthus be generated.

As far as the first-mentioned subdivision of the pin 210 into twosections is initially concerned, by virtue of the fact that one of theuniversal joints 211, 212 is arranged in a decoupled section which isseparate from the remaining part of the pin 210 and which is fixedlyfitted to the mirror, a reduction of deformation on the part of themirror 101 is obtained. This takes account of the circumstance that themirror 101 is sensitive to any introduction of force on account of theaccompanying surface deformations. This configuration is based on theconsideration that, with repeated use of the mirror 101 in measuring andmanufacturing apparatuses, a mounting of the mirror 101 that isidentical in all steps can be realized insofar as the force introductionpoint at the mirror 101 can be kept unchanged. In other words, what canbe achieved by means of the above-described division of the pin 210 intotwo is that the joint position of one of the two universal joints 211,212 remains fixed with respect to the mirror 101, since this universaljoint 211 is fixedly connected to the mirror 101. The correspondinguniversal joint 211 fixedly connected to the mirror 101 is designatedhereinafter as bush joint.

The hollow configuration of the bush joint takes account of thecircumstance that, depending on the specific conditions of use in theoptical system, a mirror can be arranged in a manner suspended from therespective actuator or else in a manner standing on the respectiveactuator.

By virtue of the fact that the bush joint is embodied in hollow fashion,by means of the linking point to the mirror it is possible to choosefreely whether the respective joint is subjected to tensile orcompressive loading, to be precise independently of how the mirror 101is arranged in the optical system. What is decisive for this is thecombination of the force direction, on the one hand, and the location ofthe fixed linking of the joint, on the other hand, which in turn isfreely selectable on account of the hollow configuration. Specifically,it is necessary to orient the force direction via the joint toward thelinking location in order that compressive loading is effected.Conversely, the force direction as viewed via the joint has to pointaway from the linking location in order that tensile loading iseffected. Therefore, once the system has been optimized with regard tothe stiffnesses and the dynamic properties, these settings can berealized or maintained both for mirror arrangements that are suspendedin the above sense and for standing mirror arrangements.

In the embodiments described above, in each case a pin with twouniversal joints is used, which transmits the movement in the verticaldirection to the mirror 101 by virtue of the fact that, via the springconnections formed by the universal joints, it couples the mirror 101 tothe moved mass of the weight force compensation device 103 and, inparticular, the associated magnetic rings 231, 232 arranged radially onthe inside from FIG. 2. In this case, as already explained, a universaljoint within the meaning of the present application is understood to bea joint which has two tilting joints with orthogonal orientation of thetilting axes with respect to one another (or tilting joints connected inseries relative to the force flux), which preferably have a common pivotpoint.

As is illustrated in FIG. 11, in practice upon application of a force oraxial loading to such a pin in conjunction with a lateral deflectionthere now occurs a transverse force F_(q) as a result of a “pendulumeffect” and moments as a result of the restoring effect/bendingstiffness of the deflected joints, which can cause e.g. deformations ofthe mirror 101 and is therefore undesirable in principle. This parasitictransverse force can be described mathematically with reference to thevariables defined in FIG. 11, as follows:

$\begin{matrix}{{F \star a} = {F_{q} \star h}} & (2) \\{F_{q} = \frac{F \star a}{h}} & (3) \\{l^{2} = {h^{2} + a^{2}}} & (4)\end{matrix}$

In this case, F denotes the force exerted on the pin 910, 1 denotes thedistance between the two universal joints of the pin, a denotes themaximum lateral deflection of the pin (or the maximum distance betweenthe laterally deflected pin and the z-axis) and h denotes the length ofthe projection of the connection path between the two universal jointsonto the z-axis.

Although, as is directly evident from equation (3), one possibleapproach for reducing the transverse force consists in increasing thelength of the pin (or the distance between the two universal joints),this is possible only to a limited extent with regard to the restrictedstructural space.

An explanation is given below, with reference to FIG. 12 aff., ofembodiments of the invention which enable the transverse forcesdescribed above to be reduced and ideally completely eliminated.

In this case, according to the invention, in order to reduce thetransverse force, use is made of the magnetic circuit already present inthe weight force compensation device explained in the embodimentsdescribed above, said magnetic circuit being composed of two magnetssituated on the inside in the radial direction and one magnet situatedon the outside in the radial direction. This is effected in a mannersuch that said magnetic circuit, by means of suitable configuration ofthe guides of said magnets, not only generates a force acting in thevertical direction, but also, as described below, generates forces ormoments which act in other directions and which are directed exactlyopposite to said transverse force F_(q) and are suitable for thecompensation thereof.

In this case, the invention is based on the concept, for instanceproceeding from the construction from FIG. 8, of deliberately making itpossible to displace the magnets 831, 832 situated on the inside in theradial direction relative to the magnets 833 situated on the outside inthe radial direction and of using this movement or the in principleparasitic forces associated therewith in as much as the transverseforces generated thereby at least partly compensate for said parasitictransverse force F_(q) acting on the pin 810.

For elucidation purposes, FIGS. 12 a and 12 b firstly show schematicbasic diagrams. In accordance with FIG. 12 a, in principle thetransverse force compensation according to the invention is achieved byvirtue of the fact that an axial guide 901 (symbolized in FIG. 12 a bythe gap or distance between the system, assumed to be stationary, andthe linking point) and a rotary joint 902 are provided on that side ofthe weight force compensation device 930 which faces away from themirror 101.

In an embodiment illustrated schematically in FIG. 12 b, it is possibleto use, in particular, a combination of a parallel guide 901 and auniversal or cardan joint 902, wherein the parallel guide 901 can beformed e.g. by two leaf springs 901 a, 901 b having e.g. theconstruction described with reference to FIGS. 5 a and 5 b, and FIGS. 6a and 6 b, respectively.

In a further embodiment, it is possible to provide, for instance, asuitable leaf spring element configured such that, in order to obtainthe compensation described above, both a deflection movement along thez-axis and a tilting about the x- or y-axis are permitted. For thispurpose, the leaf spring elements can be configured as shown in FIGS. 5a, 5 b, 6 a and 6 b, as a result of which the required degrees offreedom can be provided. In accordance with a further possibleconfiguration, it is also possible to provide an axial guide as in thecase of the weight force compensation device, in which two leaf springjoints as shown in FIGS. 5 a, 5 b, 6 a and 6 b are connected in serieswith an additional cardan joint.

The specific arrangement of the components shown in FIGS. 12 a-b isdependent on whether the relevant mirror 101 is arranged in a mannerstanding or suspended in the system.

FIG. 13 a firstly shows a specific exemplary embodiment of a standingmirror arrangement. In accordance with FIG. 13 a, analogously to theconstruction from FIG. 8, two magnets 931, 932 situated on the inside inthe radial direction form the moved mass of the weight forcecompensation device, and the outer magnet 933 in the radial directionforms the stationary part with respect to the optical system.

In contrast to the construction from FIG. 8, however, in which themagnets 831, 832 situated on the inside in the radial direction performonly a movement in the axial direction or z-direction on account of thetwo leaf spring elements 821, 822, the arrangement in accordance withFIG. 13 a is configured such that, in addition to an axial displacementin the z-direction, a torsion or tilting about the y- or x-axis (oranother axis of rotation lying in the x-y plane) is also permitted, asufficient stiffness simultaneously being present relative todisplacements laterally or in the radial direction.

For this purpose, the linking of the moved mass of the weight forcecompensation device is effected in accordance with the diagram from FIG.12 a via a suitable leaf spring element 940 configured such that both adeflection movement along the z-axis and a tilting about the x- ory-axis are permitted.

FIG. 13 b shows a further exemplary embodiment, which, in principle, isanalogous to the example from FIG. 13 a but intended for a suspendedmirror arrangement (such that the mirror 101 is arranged “at the bottom”in FIG. 13 b). Analogously to the arrangement from FIG. 13 a, in FIG. 13b the linking of the moved mass of the weight force compensation deviceor of the magnets 931, 932 lying radially on the inside to the frame 105or the stationary optical system is situated on that side of the weightforce compensation device 930 which faces away from the mirror 101.

Generally, the linking of the moved mass of the weight forcecompensation device or of the magnets 931, 932 lying radially on theinside to the frame 105 or the stationary optical system is effected insuch a way as to result in a compensation of the transverse force F_(q)acting on the pin.

For illustration purposes, FIG. 14 indicates merely schematically therespectively resulting forces and moments in the case of a displacement(not effected solely along the z-axis) of the moved mass of the weightforce compensation device or of the magnets 931, 932 lying radially onthe inside relative to the frame 105 or the stationary optical system.If, by way of example, in FIG. 14, the moved mass of the weight forcecompensation device is displaced “obliquely upward” or “obliquelydownward”, then the forces indicated by rectilinear arrows in FIG. 14and the moments indicated by curved arrows respectively have an effect(their magnitude being dependent in each case on the leverage ratios).In this case, it is assumed that in the starting position or zeroposition of the pin 910, ideally no transverse force arises (since thelatter is generated only upon deflection relative to the z-axis).According to the invention, said transverse force is now used, asdescribed above, to compensate for the described transverse force F_(q)acting on the pin 910.

Calculations show that this measure can yield reductions in theparasitic transverse force F_(q) which are of the order of magnitude of30% or more.

A further advantage of the embodiments described with reference to FIGS.12 a-12 b-13 a-13 b-14 is that only a single rotary joint (which isdesignated by 111 in FIG. 12 a and FIG. 12 b) is situated between themoved mass of the weight force compensation device or the magnets 931,932 lying radially on the inside, on the one hand, and the mirror 101,on the other hand, in contrast for instance to the embodiment from FIG.8, which has the consequence that overall the natural frequencies andstiffnesses sought can be achieved more simply compared with anarrangement composed of two rotary joints in the region between movedmass of the weight force compensation device and mirror (the axialstiffness becomes significantly higher on account of the omission of ajoint, such that the remaining universal joint can be adaptedcorrespondingly more simply).

The invention further relates to an arrangement for mounting an opticalelement as defined in the following Clauses:

1. Arrangement for mounting an optical element, in particular in an EUVprojection exposure apparatus, comprising a weight force compensationdevice for exerting a compensation force on the optical element, whereinsaid compensation force at least partly compensates for the weight forceacting on the optical element, and at least two actuators which eachexert a controllable force on the optical element, wherein at least oneof the actuators generates the controllable force on the optical elementin the direction of the compensation force.

2. Arrangement according to Clause 1, characterized in that said atleast one actuator is integrated into the weight force compensationdevice.

3. Arrangement according to Clause 1 or 2, characterized in that theweight force compensation device has a passive magnetic circuit forgenerating a constant force component of the compensation force actingon the optical element.

4. Arrangement according to any of Clauses 1 to 3, characterized in thatthe actuator acting in the direction of the compensation force, or theweight force compensation device, has at least one coil to which anelectric current can be applied and which serves for generating anactively controllable force transmitted to the optical element via atleast one movable actuator element.

5. Arrangement according to Clause 3 and 4, characterized in that saidat least one movable actuator element is a magnet belonging to thepassive magnetic circuit.

6. Arrangement according to any of the preceding Clauses, characterizedin that the optical element is a mirror.

7. Arrangement according to any of Clauses 3 to 6, characterized in thatthe magnetic force compensation device has an adjustment ring, which isdisplaceable in an axial direction relative to the drive direction,wherein the force exerted by the passive magnetic circuit can bemanipulated by displacement of said adjustment ring.

8. Arrangement according to any of the preceding Clauses, characterizedin that a mechanical coupling is formed between at least one of theactuators and the optical element in a manner such that, relative to thedrive axis of said actuator, the ratio of the stiffness of saidmechanical coupling in an axial direction to the stiffness in a lateraldirection is at least 100.

9. Arrangement according to any of the preceding Clauses, characterizedin that a mechanical coupling is formed between at least one of theactuators and the optical element in a manner such that, for saidmechanical coupling, the natural frequency in an axial direction is atleast three times the bandwidth of the regulation.

10. Arrangement according to any of the preceding Clauses, characterizedin that a mechanical coupling is formed between at least one of theactuators and the optical element in a manner such that, for saidmechanical coupling, the natural frequency in an axial direction is inthe range of 600 Hz to 1800 Hz, in particular in the range of 800 Hz to1400 Hz, more particularly in the range of 1000 Hz to 1200 Hz.

11. Arrangement for mounting an optical element, in particular in an EUVprojection exposure apparatus, comprising at least two actuators whicheach exert a controllable force on the optical element, wherein amechanical coupling is formed between at least one of the actuators andthe optical element in a manner such that, relative to the drive axis ofsaid actuator, the ratio of the stiffness of said mechanical coupling inan axial direction to the stiffness in a lateral direction is at least100.

12. Arrangement for mounting an optical element, in particular in an EUVprojection exposure apparatus, comprising at least two actuators whicheach exert a controllable force on the optical element, wherein amechanical coupling is formed between at least one of the actuators andthe optical element in a manner such that, for said mechanical coupling,the natural frequency in an axial direction is in the range of 600 Hz to1800 Hz, in particular in the range of 800 Hz to 1400 Hz, moreparticularly in the range of 1000 Hz to 1200 Hz.

13. Arrangement according to any of Clauses 8 to 12, characterized inthat the mechanical coupling has a pin provided with two universaljoints.

14. Arrangement according to Clause 13, characterized in that the pinhas a first partial element, in which one of the two universal joints isformed, and also a second partial element, which is connected to thefirst partial element in a releasable manner and in which the other ofthe two universal joints is formed.

15. Arrangement according to Clause 14, characterized in that the firstpartial element is fixedly fitted to the mirror.

16. Arrangement according to any of Clauses 13 to 15, characterized inthat at least one of the two universal joints is embodied in a hollowfashion in regions.

17. Arrangement according to any of the preceding Clauses, characterizedin that a movable actuator component of at least one of the actuators ismechanically coupled to a non-movable actuator component of saidactuator by means of a parallel spring system.

18. Arrangement according to Clause 17, characterized in that, for saidmechanical coupling, the ratio of the stiffness in a lateral directionto the stiffness in an axial direction is at least 3000, in particularat least 6000, more particularly at least 9000.

19. Arrangement according to Clause 17 or 18, characterized in that theparallel spring system has an arrangement composed of two leaf springs,which have in each case bending beams arranged tangentially relative tothe drive axis of the actuator.

20. Arrangement according to Clause 19, characterized in that at leastone of said leaf springs has bending beams running in a radial directionrelative to the drive axis of the actuator.

21. Arrangement for mounting an optical element in an optical system, inparticular in an EUV projection exposure apparatus, comprising a weightforce compensation device for exerting a compensation force on theoptical element, wherein said compensation force at least partlycompensates for the weight force acting on the optical element, whereinthe weight force compensation device has at least one magnet which ismovable relative to a stationary frame of the optical system and atleast one magnet which is stationary relative to said frame, and whereinthe at least one magnet which is movable relative to the frame ismounted in movable fashion in a direction that deviates from thedirection of the compensation force.

22. Arrangement according to Clause 21, characterized in that the weightforce compensation device is mechanically coupled to the optical elementby means of a pin.

23. Arrangement according to Clause 22, characterized in that the atleast one magnet which is movable relative to the frame is mounted inmovable fashion in a direction non-parallel to the longitudinal axis ofthe pin.

24. Arrangement according to Clause 22 or 23, characterized in that adeflection of the pin in a direction that deviates from the direction ofthe compensation force leads to a relative movement between the magnetwhich is movable relative to the frame and the magnet which isstationary relative to the frame.

25. Arrangement according to Clause 24, characterized in that saidrelative movement generates a magnetic moment which at least partlycompensates for a transverse force acting on the pin in a direction thatdeviates from the direction of the compensation force.

26. Arrangement according to any of the Clauses 21 to 25, characterizedin that a mechanical coupling is provided between the frame and themagnet which is movable relative to the frame, said mechanical couplingenabling both an axial displacement of the magnet which is movablerelative to the frame in the direction of the weight force and a tiltingof the magnet which is movable relative to the frame about a rotationalaxis perpendicular to the direction of the weight force.

27. Arrangement according to Clause 26, characterized in that saidmechanical coupling has an axial guide and a rotary joint.

28. Arrangement according to Clause 27, characterized in that the axialguide is formed by a parallel spring system composed of two leafsprings.

29. Arrangement according to Clause 26, characterized in that saidmechanical coupling has a spring element, which enables both an axialdisplacement of the magnet which is movable relative to the frame in thedirection of the weight force and a tilting of the magnet which ismovable relative to the frame about at least one rotational axisperpendicular to the direction of the weight force.

30. Arrangement according to Clause 29, characterized in that themechanical coupling formed by said spring element has a naturalfrequency in the axial direction in the range of 600 Hz to 1800 Hz, inparticular in the range of 800 Hz to 1400 Hz, more particularly in therange of 1000 Hz to 1200 Hz.

31. Arrangement according to any of Clauses 22 to 30, characterized inthat the pin has two universal joints.

32. Arrangement according to any of Clauses 21 to 31, characterized inthat the optical element is a mirror.

Even though the invention has been described on the basis of specificembodiments, numerous variations and alternative embodiments, e.g.through combination and/or exchange of features of individualembodiments, are evident to the person skilled in the art. Accordingly,for the person skilled in the art it goes without saying that suchvariations and alternative embodiments are concomitantly encompassed bythe present invention, and the scope of the invention is restricted onlywithin the meaning of the accompanying patent claims and the equivalentsthereof.

1.-25. (canceled)
 26. An arrangement, comprising: a weight forcecompensation device configured to exert a compensation force on anoptical element to at least partly compensate a weight force acting onthe optical element, wherein: the weight force compensation devicecomprises a passive magnetic circuit configured to generate a forcecomponent of the compensation force; and the weight force compensationdevice comprises an adjustment element configured so that the forcecomponent of the compensation force is continuously adjustable.
 27. Thearrangement of claim 26, wherein the adjustment element is displaceablein an axial direction relative to a direction of the compensation force,and the force component is manipulable via the displacement.
 28. Thearrangement of claim 26, wherein the adjustment element comprises a softmagnetic material.
 29. The arrangement of claim 26, wherein theadjustment element comprises a permanent magnet.
 30. The arrangement ofclaim 26, wherein the adjustment element comprises a coil configured tohave an electric current applied thereto.
 31. The arrangement of claim26, wherein the adjustment element at least partly surrounds the weightforce compensation device.
 32. The arrangement of claim 26, wherein theadjustment element has a ring-shaped geometry.
 33. The arrangement ofclaim 26, further comprising a control system, wherein a position of theadjustment element is controllable via the control system depending onat least one operation parameter of the arrangement.
 34. The arrangementof claim 33, wherein a temperature-induced or ageing-induced change ofthe compensation force is reducible compared to an analogous arrangementwithout the control system.
 35. The arrangement of claim 26, furthercomprising at least two actuators configured to exert a controllableforce on the optical element, wherein at least one of the at least twoactuators is configured to generate the controllable force on theoptical element in a direction of the compensation force.
 36. Thearrangement of claim 35, wherein the at least one actuator is integralwith the weight force compensation device.
 37. The arrangement of claim35, wherein the at least one actuator or the weight force compensationdevice comprises a coil to which an electric current is applicable andwhich is capable of generating an actively controllable forcetransmitted to the optical element via at least one movable actuatorelement.
 38. The arrangement of claim 37, wherein the at least onemovable actuator element comprises a magnet which is an element of apassive magnetic circuit.
 39. The arrangement of claim 35, comprising amechanical coupling between at least one of the actuators and theoptical element so that, relative to a drive axis of the at least oneactuator, a ratio of a stiffness of the mechanical coupling in an axialdirection to a stiffness of the mechanical coupling in a lateraldirection is at least
 100. 40. The arrangement of claim 35, comprising amechanical coupling between at least one of the actuators and theoptical element so that the mechanical coupling has a natural frequencyin an axial direction that is at least three times a bandwidth of aregulation.
 41. The arrangement of claim 35, comprising a mechanicalcoupling between at least one of the actuators and the optical elementso that that the mechanical coupling has a natural frequency in an axialdirection which in a range of 600 Hz to 1800 Hz.
 42. The arrangement ofclaim 35, wherein the mechanical coupling comprising a pin comprisingfirst and second universal joints.
 43. The arrangement of claim 42,wherein the pin comprises a first partial element comprising the firstuniversal joint, the pin comprises a second partial element connected tothe first partial element in a releasable manner, and the second partialelement comprises the second universal joint.
 44. The arrangement ofclaim 43, wherein the first partial element is fixedly fitted to theoptical element.
 45. The arrangement of claim 42, wherein the firstuniversal joints has hollow regions.
 46. The arrangement of claim 35,wherein at least one of the actuators comprises a movable actuatorcomponent and a non-movable actuator components, and the movableactuator component is mechanically coupled to the non-movable actuatorcomponent via a parallel spring system.
 47. The arrangement of claim 46,wherein the mechanical coupling has a ratio of a stiffness in a lateraldirection to a stiffness in an axial direction of at least
 3000. 48. Thearrangement of claim 46, wherein the parallel spring system comprises anarrangement comprising two leaf springs, each leaf spring comprisingbending beams arranged tangentially relative to a drive axis of the atleast one actuator.
 49. The arrangement of claim 46, wherein at leastone of the leaf springs comprises bending beams that run in a radialdirection relative to the drive axis of the at least one actuator. 50.The arrangement of claim 26, wherein the optical element comprises amirror.
 51. The arrangement of claim 26, further comprising the opticalelement.
 52. A lens, comprising: an optical element; and a weight forcecompensation device configured to exert a compensation force on theoptical element to at least partly compensate a weight force acting onthe optical element, the weight force compensation device comprising apassive magnetic circuit configured to generate a force component of thecompensation force, and the weight force compensation device comprisingan adjustment element configured so that the force component of thecompensation force is continuously adjustable, wherein the lens is anEUV projection lens.
 53. An apparatus, comprising: an illuminationdevice; and a projection lens, comprising: an optical element; and aweight force compensation device configured to exert a compensationforce on the optical element to at least partly compensate a weightforce acting on the optical element, the weight force compensationdevice comprising a passive magnetic circuit configured to generate aforce component of the compensation force, and the weight forcecompensation device comprising an adjustment element configured so thatthe force component of the compensation force is continuouslyadjustable, wherein the apparatus is an EUV projection exposureapparatus.